1. Field of the Invention
The present invention relates to a sliding material consisting of a carbon-fiber reinforced carbon composite material having a high friction coefficient and excellent wear resistance.
2. Description of the Background
A carbon-fiber reinforced carbon composite material (hereinafter referred to simply as C/C composite material) is usually produced by impregnating or mixing a resin to a carbon fiber aggregate, followed by heating forming, or by baking a carbon fiber structure (carbon fiber preform) in a non-oxidizing atmosphere and densifying it, followed by graphitizing treatment as the case requires. The C/C composite material has conventionally been used as a material for e.g. sliding members, drive joints or braking mechanism, as a material which has a high specific strength, which is light and which can be used at a high temperature. It has attracted attention particularly as a sliding material for e.g. a brake and clutch of aircraft, public vehicles and racing vehicles.
When the C/C composite material is used as a sliding material, it is used under heavy load conditions of high temperature and high pressure, and accordingly various methods to increase the friction coefficient and wear resistance have been proposed.
Among them, many methods to cover the surface of the C/C composite material with a SiC layer by means of e.g. a vapor-phase growth method such as a CVD method, a coating method or an impregnation method, have been proposed. However, although the sliding material obtained by this method has improved wear resistance, it tends to have a low friction coefficient. Further, its bulk density tends to be high, thus impairing weight savings, and further, the production costs tend to be high.
On the other hand, it has been known that a sliding material excellent in wear resistance can be obtained by a method of adding fine particles of an inorganic substance having a Knoop hardness of at least 300 kg/mm2 to a carbon fiber preform, followed by forming, baking and densifying (JP-A-7-101783). However, although the sliding material obtained by this method has improved wear resistance, the improvement of the friction coefficient is insufficient.
In a case where the C/C composite material is used as a sliding material for e.g. a brake or clutch, particularly as a brake material or a clutch material for racing vehicles, a sliding material having a high friction coefficient is required for deceleration in a short time or so as to decrease the sliding area. Further, at the time of sliding under a heavy load, the temperature of the sliding material tends to be high, and the friction coefficient tends to decrease by fading, such being problematic. Thus, it is an object of the present invention to provide a sliding material consisting of a C/C composite material which is light and excellent in wear resistance, and which has a high friction coefficient even under a heavy load.